Curtains used for shading or decoration in residence or offices have been presently popularized. In respect to the way for drawing or furling the curtains, mostly, cords are used for drawing or furling the curtains. However, the curtains are applicable to venetian blinds or curtains drawn and furled toward left and right sides, but not applicable to a one-piece shade. Therefore, the inventor researched, developed and tested a shade device with particular effect. This shade device is provided, at left side of a rail, with a drawing and furling device, which is pulled once for drawing a shade cloth clockwise downwardly and is pulled again for furling the shade cloth counter-clockwise upwardly. When the shade cloth is being furled, it is furled in a gentle manner via a buffer device provided at right side of the rail. However, it is apt to generate noise when the shade cloth is being furled, due to a high coefficient of friction within the buffer device, and thus an increased friction force generated correspondingly.
For the prevention of unduly large noise, Taiwan patent no. 484397, titled “Improvement on buffer device for furl of shade”, was filed by the inventor. Referring to FIGS. 1-4, a shade device 1 of that application is constituted by a rail 11, an adjustment device 12, a buffer device 13, a drawing and furling device 14 having an elastic element 141, and a shade cloth 15. In this case, the buffer device 13 includes a housing body 130, a covered cylinder 131 coveredly provided within the housing body 130, a covering body 132 covered inside the covered cylinder 131 and provided at one end thereof with a guide rod 1321, a cap body 133 coveringly provided between the covered cylinder 131 and the housing body 130, respectively, to be coveringly secured and integrated therewith, and a rotating block 134 embeddedly combined with the guide rod 1321 of the covering body 132. Further, lubricating oil injected into the inner edge of the housing body 130 of the buffer device 13 is operated as drag. Thereby, when the shade cloth 15 is being furled, large noise generated due to a high coefficient of mutual friction is not resulted and auditory sensation is then not affected.
It is found that noise generated due to a high coefficient of friction, when the shade cloth 15 is being furled may be avoided in the buffer device 13 of that application. However, a shaft rod 135 is formed within the covered cylinder 131 and a spring 136 is provided around the shaft rod 135. Then, the outer diameter of the covered cylinder 131 should be enlarged, and the enlarged diameter of the covered cylinder 131 is then provided for the spring 136 to be coveredly provided inside. Hence, after the outer diameter of the spring 136 and that of the covered cylinder 131 are added together, the outer diameter of the whole assembled buffer device 13 is further enlarged when the covered cylinder 131 is covered inside the housing body 130 (as illustrated in FIG. 4). Moreover, the manufacturing cost is high. Therefore, it is simple to enlarge the outer diameter of the buffer device 13, while the reduction in the outer diameter of the buffer device 13 is extremely limited. Therefore, it is only possible for the buffer device 13 of that application to be mounted in the shade device 1 used on the door/window, while it is difficult to install this shade device 1 in the small-sized roller shade used within the car door of limited thickness.